Conventionally, known is an object detection device which detects objects using detection beams such as infrared rays (IR). Such an object detection device is provided with a detection unit composed of, for example, a light emitter which emits detection beams to a detection area and a light receiver which is disposed to oppose the light emitter and which receives the detection beams to output detection signals. The object detection device detects an object from a change in the amount of the detection beams (detection signal level) received by the light receiver, which change is caused when the object intercepts the beams.
In recent years, for the purpose of reduction in power consumption, time and effort for wiring, an increased number of object detection devices have been designed to be driven by batteries mounted inside the devices. In such devices, there sometimes occurs a so called a reverse connection, in which a battery is mounted into a battery holder with the predetermined polarity reversed by mistake. In this case, not only it is impossible to normally supply power to the device to enable detection operation, but also damage can be caused to the electric circuit of the device.
As an example of a structure for preventing the reverse connection, a battery holder which prevents reverse mounting of a battery 10 is known (JP Laid-open Patent Publication No.2000-82450), as shown in FIG. 7. The structure includes a holding member 50 to which a ring-shaped resin insulator 55 is provided so that the center hole 56 of the insulator 55 is aligned with a positive electrode contact portion 51 of the holding member 50. The insulator 55 allows a projecting positive electrode 11 of the battery 10 to enter into the hole 56, but prevents the battery 10 from being energized when the negative electrode 12 is mounted onto the positive electrode contact portion 51 due to reverse mounting of the battery 10.
As the battery 10 to be used for the device, various shapes of batteries are sold on the market. For example, as shown as a in FIG. 7, there is a battery whose positive electrode has a relatively lower projection height H of, for example, less than 0.5 mm, as compared to a projection height H0 of the standard positive electrode 11 from its end face. However, if the resin insulator 55 is produced by plastic injection molding, a limit of the thickness of the resin to be moldable is 0.5 to 0.6 mm. If the height of the projecting positive electrode 11 is less than 0.5 mm, since the thickness of the insulator 55 exceeds the height, the positive electrode 11 of the battery 10 cannot come in contact with the positive electrode contact terminal 51 of the holding member 50. Consequently contact failure will be caused. Accordingly, there have been cases where the types of batteries usable for the object detection device are limited.
Further, even in the case where the height of the positive electrode 11 is 0.5 mm or more, if the battery 10 has an outer covering member 15 which covers the entire side surface and the outer circumferences of the end surfaces of the battery, as shown in FIG. 8, and if an outer circumference covering portion 15a of the outer covering member 15 has a thickness T in the axial direction of the battery 10, then the substantial height of the positive electrode 11 of the battery 10, that is the distance between the surface of the outer circumference covering portion 15a and the end face of the positive electrode 11, lowers, and consequently contact failure will be caused similarly.